A study to constrain the geometry of an active fault in southern Italy through borehole breakouts and downhole logs.

Simona Pierdominici (1) , Maria Teresa Mariucci (1) , Paola Montone (1)

1 Istituto Nazionale di Geofisica e Vulcanologia

Identification of an active fault and the local versus regional present-day stress field in the Irpinia region (southern Apennines) have been performed along a 5900m deep well (San Gregorio Magno 1) by a detailed breakout and geophysical log analysis. The selected area is characterized by diffuse low magnitude seismicity, although in historical times moderate to large earthquakes have repeatedly struck it. On 23 November 1980 a strong earthquake (M=6.9) nucleated on a 38km-long normal fault, named Irpinia fault, producing the first unequivocal historical surface faulting ever documented in Italy. The analysis of stress-induced wellbore breakouts shows a direction of minimum horizontal stress N18°±24°, fairly consistent with the regional stress trend (N44°±20°). The small discrepancy between our result and the regional stress orientation might be related to the influence of local stress sources such as variations of the Irpinia fault plane orientation and the presence of differently oriented active shear zones. This paper shows for the first time a detailed analysis on the present-day stress along a well to identify the Irpinia fault at depth and constrain its geometry.

Mots clés: Borehole breakout; geophysical log; present-day stress field; seismogenic fault; southern Apennines; Italy.; Italy

Domaines: Sciences de la Terre

Simona Pierdominici, Maria Teresa Mariucci, Paola Montone. A study to constrain the geometry of an active fault in southern Italy through borehole breakouts and downhole logs.. Journal of Geodynamics, 2011, 52 (3-4), pp.279. ⟨10.1016/j.jog.2011.02.006⟩. ⟨hal-00780027⟩